420 



THE RABBIT. PHYLUM CHORDATA 



■p.TTied,. 



In the trunk (Fig. 332) they are arranged in the form of a tube, 

 which encloses a large space, the body cavity or coelom. On the 



dorsal surface this tube is very 

 much thicker than elsewhere, and 

 the muscles here surround the 

 backbone and the limb girdles. The 

 coelom is lined by a membrane, 

 the peritoneum, which is con- 

 tinued over the surface of the 

 intestine and other organs (the 

 viscera) which the coelom contains. 

 The viscera are in fact not strictly 

 in the coelom, but slung from its 

 roof by folds in the lining of the 

 roof itself (Fig. 333). As the gut 

 comes to be very much longer 

 than the coelom the folds are very 

 difficult to follow in the adult 

 animal. Those which sling the 

 stomach, liver, duodenum and 

 spleen are called omenta, and those 

 supporting the rest of the gut 

 mesenteries. The coelom is divided 

 into two by a vertical muscular 

 partition, the midriff or diaphragm, which separates off from the 

 peritoneal cavity of the abdomen a chest or thorax in the breast 



~a^.?TvecL. 



A diagram of a trans- 



FiG. 332. 



verse section through 

 thorax of a rabbit. 



the 



a.med.. Ventral part of mediastinum ; ao. 

 aorta ; i.v.c, inferior vena cava ; l.v. 

 left ventricle ; as., oesophagus : p.c. 

 pericardial cavity ; p.med., dorsal part 

 of mediastinum ; pm., pericardium ; 

 r.l., right lung ; r.pL, right pleura ; 

 r.pl.c, right pleura] cavity ; r.v., right 

 ventricle ; xp.c, spina cord ; st., sternum; 

 v., vertebra. 



A B C 



Fig. 333. — A diagram of the perivisceral coelom in transverse section : ^, of the 

 dogfish ; B, of the frog ; C, of the rabbit or man. 



d., Diaphragm ; h., heart ; /., lung ; p.c, peritoneal cavity ; pl.c, pleural cavity ; 

 pi. p.c, pleuroperitoneal cavity ; pec, pericardial cavity. 



region, where Hes the pericardium, with on each side a pleural 

 cavity, into which the lung of its side projects. The lining of 



